Traveling wave amplifier



Sept. 8, 1953 A. G. CLAVIER ETAL TRAVELING WAVE AMPLIFIER Filed March 27, 1947 2 sheets-sheet 1 Evl l* l my 2 N IN V EN TORS 'fr/MNE am mma/2,540

Sept. 8, 1953 A. G. CLAVIER ETAL 2,651,585

TRAVELING WAVE AMPLIFIER Filed March 27, 1947 2 Sheets-Sheet 2 IN V EN T ORS KIND/PE G. CZ /4 V/EP E/ENNE C. 0E W'MMEKIU in one direction, and to have selective amplifying Y powers for waves of different selected frequency Patented Sept. 8, 1953 TRAVELIN G WAVE AMPLIFIER Andr G. Clavier and Etienne C. de Faymoreau, New York, N. Y., assignors to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application March 27, 1947, serial No. 737,602

-This invention relates to wave transmission systems and more especially to systems for thev A principal object of the invention is to pro-A vide a wave transmission system wherein at least one electron discharge device is employed, the' electron trajectories within the device and the initial electron velocity being correlated with the electric eld between the transmission line conductors at the region where the device is connected, so as to achieve selective frequency amplification of waves in a given frequency range which are propagated in one direction along the line, as compared with waves of the same frequency range propagated along the line in the opposite direction.

Another object is to provide an improved electron tube of the travelling wave type which has asymmetrical transmission characteristics for the same frequency range to be vpropagated through the device in opposite directions.

Another object is to provide an improved twoway high frequency wave transmission system employing one or more travelling wave tubes of novel construction.

Another important object is to provide an electron tube of the travelling wave type having means to control its transmission properties by controlling the electron trajectories from the cathode so as to impart asymmetrical conductive properties to the tube when it is used as a high frequency transmission line section. l

A feature of the invention relates to a high frequency transmission line unit comprised of ai i convoluted transmission line section between the conductors of which an electron discharge is set up, and means are provided to adjust the electron trajectories at a predetermined angle to the wave propagaticnal axis of the line to impart to said line section selective amplifying properties for waves of a selected frequency range.

Another feature relates to an electron discharge tube enclosing an electron emitter which is surrounded by a convoluted transmission line together with means to adjust the initial velocity and trajectory of the electron stream between the line conductors within the tube to cause the tube to have selective amplifying powers for waves of a selected frequency propagated along the line 7 Claims. (Cl. 179-171) propagated along the line in the opposite direction.

Another feature relates to an electron tube of.

the. ytravelling wave Vtype wherein an electron emitter is provided with a pair of cooperating electrodes which form a convoluted transmission line.

A further feature relates to an electron tube having an elongated central emitting cathode which is surrounded by a convoluted transmission line section, the outer conductor of the said line section being tubular and having that portion of its periphery near the cathode, of open- Work construction.

A further feature relates to a novel construction of electron tube which has the property of actingas a two-way amplifier without danger of singing.

A still further feature relates to the novel arrangement and correlation of parts and electric parameters for producingan improved two-way ultra highy frequency wave transmission and amplifying system.

Other features and' advantages will appear from the following detailed descriptions and the appended claims.

In the drawing,

* Fig. 1 is a schematic diagram of a generic high frequency wave transmission system to which the invention is applicable.

Fig. 2 is a schematic diagram of a system according to the invention and showing thenovel travelling wave tube which also forms part of the invention.

Fig. 3 is a detailed view of the convoluted transmission line section of the tube of Fig. 2.

Fig. 4 is an end view of the tube of Fig. 2.

Fig. 5 is an enlarged perspective view of part of Fig. 2.

Fig. 6 is a schematic illustration of a modification of the tube of Fig. 4.

Fig. '7 is a modification wherein the signal transmission is effected by an electrode acting as a Wave guide. f

Referring to Fig.. 1, thereis shown in schematic form, the general type of system to which the present invention is applicable. It comprises a source l0 of high frequency wave energy, a high frequency load device lland an intervening transmission line l2. The load device is matched to the surge impedance-of the transmission line so as to avoid the setting up of standing waves ,therealong Interpo'sed in this line at any suitample through the intermediary of the overlapping quarter-wave line sections I'I, I8; and member I is connected as an effective continuation of the other line conductor. Preferably, a1- though not necessarily, the members I5 and I6 are at the same D. C. potential, and the cathode id is negatively biassedE with respect thereto so as to impart-a predetermined initialelectron velocity to the electrons which travel transversely between the electrodes I5 and IB. With this arrangement the transmission line conductors can be held at D. C. ground potential. If the physical length of the members I5t and t6, con sidered as reflectionless extensions of. the transmission line conductors, is substantially greater; than the wave length of the waves from sourcey I6, then by interaction between the. electric field. of these waves and the electrons between the transmission line conductors within the tube i3, these waves are boosted in amplitude. By adjusting the ini-tial. velocity and transitv timek of the electrons, there is produced., a negative lea-kance effect along theline at the reg-ion where device I3 is located. For a detailed description of. this type of transmission lineY arrangement, reference may be. had to application Serial No.. 726,343; led. February 4,. 14947, now abandoned.

The tube I3 operates as an amplifier equally well in both directions, but itnecessitates. very good impedance matching atA both. ends of. the

device I3 with the respective transmission lineV sections. More precisely; when the reflected portion of a travelling wave propagated along the line happens to fall in phase with the incoming wave at the input of tube I3, the condition for stability will be in which A is the volt amplification. ratio of the tube, and r the reflection coeifcient at. the. output end of theV tube. This, meansA that if' the matching can be arrangedr sol that. r=.01,. A.cannot exceed 10. In order to overcome this limitation, and in accordance with this invention, the. electrons from4 cathode` IAT Ytraversing the space between I5 and.. I6 have.. a predetermined initial velocity having an` axial` component considered. along the propagational. axis of the transmissionv line.

A theoreticalA investigation shows that asa first. approximation, the same negative leakance effects can be. obtained as in. the arrangement of application Serial No... '1126,343, but the frequencies limiting the: regions where such. an eiiect is obtained, are determinedV by the following expressions:

E jfr=1 vnu-m) 2 2 while in the previous case the corresponding formulae were:

In these equations l is the distance between the conductors of the transmission line, um; is the initial speed of electrons in the direction per."- pendicular to the axis of' the line, and. m1 is the ratio of the initial speed of electrons. in the axial. direction to the speedl of travelling wave,

For the wave travelling in the opposite direction, the same formulae will apply except that l-m will become l-I-m. A suitable choice for factor m will thus provide a means to separate the range of frequencies which is amplified in one direction, say east to West, from the range of frequenciesV which will' be ampliiiiedl the reverse direction', say west to. east. The best initial velocity is at 45" to the direction of the propagational axis of the line, in order to bring the effect of the magnetic eld of the travelling waveincooperative phase with the effect of the electric. iield;

Referring to Figs; 2 to 5, there is shown one 1 preferredl arrangement for controlling the initial electron velocities and trajectories to achieve the desired.. asymmetric transmission characteristics. In Fig. 2, the source I0 of ultra frequency wave signalsi'sf connected to the load I I via transmission line I2, which is preferably of the coaxial or Wave guide type. Interposed in, and. forming part ofthis. transmission line is an electron discharge tube 2.! which, accordingV tothe invention, comprises an evacuated glass envelope or' bulb 2.2 having centrally supportedtherein an electronemitting cathodev sleeve 23, provided with an internal hea-ter wire 24. in the manner well-known in electron tubes of the indirectly heated cathode type,

' sion line section comprising, an outer tubular or hollow` conductor 28,.within which is insulatingly supported by insulator beads 29,. the central con-f ductor 3U. If desired, the conductor 30 may have lateral. conductive uns or wings 3l, 32, to-

provide the desired capacitance between the linel conductors and thereby to effect any desired slowing down of the travelling. waves which. are' propagated.V along the line between the conductors. The wall portion. 33v of conductor 28 adjacent cathode 23 is-of open-Work construction suchas wire mesh so as to enable the electrons emitted from the cathode 23 to now between the said line conductors 30A and 33.. The members 30 and 33 are. suitably biassed with respect. tothe cathode 23', for example by the: battery 34, soas to. impart the desired initial electron velocity tor the emitted electrons. In certain special cases it may be desirable to apply a different D. C-. bias to` members 30 and 33 as indicated. by the connection to the battery 34 (Fig. 2) a positive ter-- minal of which may be grounded.

Suitably supportedwith relation to tube 22 is a magnet 35 to provide a magnetic iieldV oi constant strength. The tube 22 is supported so that the central longitudinal axis thereof is in. line withA the field between the magnet poles 36, 3T. By this arrangement the electron trajectories between line conductors 30 and 33- of this section will have the desired inclination with respect to the electrical field existing between these conductors which electricv field is of course determined: by the signals applied tothe trans:- mission line section from source I0. The said inclination of the electron trajectories will be determined by radial spacing of the cathode 23 and the conductor 3U and by the strength and direction of the magnetic neld.v As pointedl out above, if the cathode 23 and the convoluted section 28 have physical lengths which are substantially greater than. the Wave length of the sig- 'Ifhe cathode. sleeve 23. is provided with a lead-in 25 and. separate lead-ins- 25, 21 are provided: for supplying current tetheassignee nals are subjected to amplification as they are.

propagated through the tube. One possible explanation of this effect is that the average kinetic energy of the electrons during each period of the travelling wave is decreased. The corresponding loss of energy in the electron beam is transferred to the electromagnetic field of the wave which is thus amplified as it travels along the tube.

With this arrangement, the operation of 'the tube for a definite frequency range from source l may be amplified, is substantially entirely electronically controlled and the selective transmission is effected by adjusting the initial electron velocity for correct electron transit time between Athe conductors 30, 33, and by the correct initial electron direction. Preferably, the transit time is adjusted to between 21r and 31|- radians.`

While Fig. 2' shows acne-way transmission system, it will be understood that the tube 22 can be connected so as to form part of a simultaneous two-way transmission system. By the adjustment of the initial velocity of the electrons and their inclined trajectories as above described, provision can be made for a range of frequencies to be selectively amplified in the east-west direction, and a separate range of frequencies to be selectively amplified in the west-east direction, without danger of singing in the tube. Thus, the transmission line can be used in both directions in a manner analogous to two-way telephony systems. The arrangement therefore is useful in a relay station of a radio link in which case the tube 22 has the opposite ends of the convoluted transmission line section connected to suitable high frequency pick-up antennae and associated with each such antenna is a corresponding parabolic reflector.

Fig. 6 shows a modification of Fig. 5, wherein the two transmission line conductors consist of a hollow coiled tubular member 28 with the portion of its periphery facing the cathode 23 in the form of a wire mesh 30a, which mesh however is supported at its longitudinal edges by insulator beads 38, so as to be insulated from the portion 28, so far as the high frequency transmission signal currents are concerned. In other words, elements 3l a and 28 constitute a helically coiled two-conductor high frequency transmission line, the foraminous portion of which faces the cathode 23, the transmission line being suitably biassed with respect to the cathode so as to produce the desired electron velocities between elements 38a and 28. It is understood of course that a constant intensity magnetic eld is produced with respect to the electron trajectories in the same manner as illustrated in the embodiment of Fig. 2, for example by magnet 35, and the coiled line and cathode are mounted within an evacuated envelope.

The invention is not limited to a system employing a transmission line of the coaxial type, or of the two-conductor type. It is equally well applicable to a transmission line of the wave guide type. Such an arrangement is schematically illustrated in Fig. '7, in which the wave guide consists of a helically convoluted tubular member similar to the member 28 but with the cen- 6.. tral conductor 30 omitted. This coiled member coaxially surrounds the electron-emitting cathode 23, and the portion 30a of the periphery of member 28 facing the cathode is of foraminous or open-work construction such as wire mesh.

In Fig. `'7, the foraminous section 30o which faces the cathode is in D. C. conductive relation with the portion 28 to form a suitable wave guide and this wave guide is suitably biassed with respect to cathode 23 to provide the desired initial elec.- tron velocity from the cathode traversing the space between 30h and 28. It will be understood of course, .that the coiled wave guide is suitably mounted together withthe cathode in an evacul ated receptacle as in the embodiment of Fig. 2. Likewise, a constant magnetic field is provided, for example .by a magnet similar to magnet 35, to provide the necessary inclined electron trajectories.

While particular embodiments have been disclosed herein, it will be understood that various changes and'modiiications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A. device for amplifying the energy of a high frequency :wave comprising a pair of spaced conductors of elongated form, a cathode disp-osed adjacent said conductors, input coupling means to apply high frequency wave energy to said conductors for propagation therealong, output coupling means to take off wave energy from said conductors, means to bias at least one of said conductors positively with respect to said cathode to eiect a' flow of electrons between said cathode and said one conductor and means for producing a magnetic field substantially at right angles to the disposition of said conductors to effect inclination of the projectory of said electrons in a direction lengthwise of said conductors, said biasing means including connections for biasing bothof said conductors, said biasing means including means for biasing one of said conductors at a higher potential than the other.

2. A device for amplifying the energy of a high frequency wave comprising a pair of spaced con- -ductors of elongated form, a cathode disposed adjacent said conductors, input-coupling means to apply high frequency wave energy to said conductors for propagation therealong, output coupling means to take off wave energy from said conductors, means to bias at least one of said conductors positively with respect to said cathode to effect a flow of electrons between said cathode land said one conductor and means for producing a magnetic field substantially at right angles to the disposition of said conductors to effect inclination of the projectory of said electrons in a direction lengthwise of said conductors, one of said conductors being at least in part interposed between the other of said conductors and said cathode and the interposed part being foraminous to permit the passage of electrons from said cathode into the space between said conductors.

3. A device for amplifying the energy of a high frequency wave comprising a pair of spaced conductors of elongated form, a cathode disposed adjacent said conductors, input coupling means to apply high frequency wave energy to said conductors for propagation therealong, output coupling means to take off wave energy from said conductors, means to bias at least one of said conductors positively with respect to said cathode to eiect a flow of electrons between said cathode and Vsaid one conductor and meansfor pro-V ducing a magnetic field substantially at right angles to the disposition of said conductors to effeet inclination of the projectory of said electrons in a direction lengthwise of said conductors, said conductors comprising a wave 'guide with one of the conductors disposed Within the other and the side of the conductor nearest said cathode being provided with Vopeningsv therethrough for the passage of said electrons from said cathode to the inner conductor.

4.r A traveling wave amplier comprising magnetic means for producing a magnetic field, a cathode of elongated form disposed coaxially of said eld, a wave guide comprising an inner and an outer conductor disposed in the form of a helix about said cathode whereby the lines of force of said magnetic field are substantially normal to the turns of said wave guide, the side of the outer conductor adjacent said cathode being of open-Work construction for the passage of electrons and means for biasing at least one of said conductors positively with respect to said cathode.

5. A traveling wave amplifier according` to claim 4, wherein said inner conductor includes at least one vane capacitively spaced from the outer conductor.

6; Atraveling wave amplifier according toclam- 6, wherein said biasing means includes means for biasing the inner conductor at a more positire potential than said outer conductor.

vANDR: G. CLAVIER.

ETIENNE C. DE FAYMOREAU.

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